gce a level marking scheme - cherry hill tuition a2 w june 2017 unit 4 ms.pdf · wjec gce biology -...

© WJEC CBAC Ltd.

GCE A LEVEL MARKING SCHEME

SUMMER 2017 A LEVEL (NEW) BIOLOGY - UNIT 4 1400U40-1

© WJEC CBAC Ltd.

INTRODUCTION This marking scheme was used by WJEC for the 2017 examination. It was finalised after detailed discussion at examiners' conferences by all the examiners involved in the assessment. The conference was held shortly after the paper was taken so that reference could be made to the full range of candidates' responses, with photocopied scripts forming the basis of discussion. The aim of the conference was to ensure that the marking scheme was interpreted and applied in the same way by all examiners. It is hoped that this information will be of assistance to centres but it is recognised at the same time that, without the benefit of participation in the examiners' conference, teachers may have different views on certain matters of detail or interpretation. WJEC regrets that it cannot enter into any discussion or correspondence about this marking scheme.

1 © WJEC CBAC Ltd.

UNIT 4 – VARIATION, INHERITANCE AND OPTIONS

MARK SCHEME

GENERAL INSTRUCTIONS

Recording of marks

Examiners must mark in red ink.

One tick must equate to one mark (apart from the questions where a level of response mark scheme is applied).

Question totals should be written in the box at the end of the question.

Question totals should be entered onto the grid on the front cover and these should be added to give the script total for each candidate.

Marking rules

All work should be seen to have been marked.

Marking schemes will indicate when explicit working is deemed to be a necessary part of a correct answer.

Crossed out responses not replaced should be marked.

Credit will be given for correct and relevant alternative responses which are not recorded in the mark scheme.

Extended response question A level of response mark scheme is used. Before applying the mark scheme please read through the whole answer from start to finish. Firstly, decide which level descriptor matches best with the candidate’s response: remember that you should be considering the overall quality of the response. Then decide which mark to award within the level. Award the higher mark in the level if there is a good match with both the content statements and the communication statement. Award the middle mark in the level if most of the content statements are given and the communication statement is partially met. Award the lower mark if only the content statements are matched.

Marking abbreviations

The following may be used in marking schemes or in the marking of scripts to indicate reasons for the marks awarded.

cao = correct answer only ecf = error carried forward bod = benefit of doubt

2 © WJEC CBAC Ltd.

WJEC GCE BIOLOGY - HUMAN BIOLOGY SUMMER 2017

UNIT 4 MARK SCHEME

Question Marking details Marks Available

AO1 AO2 AO3 Total Maths Prac

1 (a) (i) (Genetically) Identical / clone/ the same (1) Mitosis (1)

2 2

(ii) Stigma above anthers/ anthers below stigma/ carpels above stamen/ reference to female parts above male parts/ ORA (1) NOT they are different heights

1 1

(iii) Prevent inbreeding / (Increase) genetic {variation/ diversity}/Prevent homozygosity/ description of homozygosity/ larger gene pool/ ORA (1) increase chances of survival (of plant species)/ selective advantage/ adapt to changing environment/ maintain vigour (1)

2 2

(b) (i) Gamete 10 Endosperm 30 Petal 20 3 correct = 2 marks, 2 correct = 1 mark

2 2

(ii) A.A. Chromosome number doubled / 3n to 6n/ triploid to

hexaploid/ even number of each chromosome (1)

NOT returned to diploid

B. ref to endomitosis/ cell does not divide/ non disjunction/ no

cytokinesis (1)

C. Homologous pairs/ bivalents form (1)

D. Prophase 1 (1)

E. Meiosis (1)

F. (viable) gametes can be produced (1)

4 1 5

3 © WJEC CBAC Ltd.



(b) (iii) outcompeted/ not isolated so able to breed with parental plants / loss of habitat or description of (1)

1 1

Question 1 total 4 9 0 13

4 © WJEC CBAC Ltd.



2 (a) (i) Intron {does not code / spliced out/ not translated} (1) Exon {codes/ is translated} (for a polypeptide) (1) NOT codes for an amino acid(s)

2 2

(ii) Water potential falls (in the mitochondria)/ solute potential decreases (1) Water enters by osmosis (1) Max 1 if refer to cell

2 2

(b) (i) Phenotype parents: unaffected male, {unaffected/carrier} female (1) Genotype parents, XDY , XDXd (1) Genotype gametes, XD. Y. XD. Xd (1) ECF Genotypes offspring, XD Y, XdY, XDXd XDXD (1)ECF

4 4

(ii) They could {have two copies of the healthy gene/ be homozygous dominant} or be {heterozygous / carrier}/ They could be XDXd or XDXD/ can't determine until they reproduce (1)

1 1

(c) Any 2 x (1) from: Cause immune response against virus/ antibodies may be produced against it (1) Problems introducing gene into muscle (cells)/ may not reach {target (cell)/ muscle (cell)}/ may invade {non target / host} cells(1) Virus may {become pathogenic/ cause disease/ cause infection/ destroy cells}(1) NOT harm/ illness May affect other genes/ reference to oncogenes(1)

2 2

(d) (i) CCGUUA(1) 1 1

5 © WJEC CBAC Ltd.



(ii) Shorter / different 1o structure/ less amino acids/ smaller/ ORA (1)

1 1

(iii) do not have to repeat treatment/ more permanent treatment/ change present in daughter cells/ change present after cell replicates/ can pass to next generation (1)

1 1

(iv) Unknown long-term effects /possible activation of oncogenes / modified gene passed on to next generation/ affect {other genes/ later generations}(1)

1 1

(e) Not sex linked / on autosomes (1) Dominant/not recessive (1) Three examples to justify the conclusions for (3) If recessive 1 + 2 could not produce 6/ unaffected {female/ child} 8 + 9 could not produce 13 /14/ unaffected {female/ child} OR must be dominant, otherwise all children of 1+ 2 / 8 + 9 would be affected If sex linked 1 + 2 could not produce 6/ unaffected female 8 + 9 could not produce 13 or 14/ unaffected female 4 + 5 could not produce 10/ an affected male OR must be autosomal, otherwise all daughters of 1+ 2 / 8 + 9 would be affected Max (4) if examples are given to only support one conclusion.

5 5


6 © WJEC CBAC Ltd.

Question Marking details Marks available


3 (a) (i) Allow 25.4/ 25.6 / 26.0/ 26.3/ 26.25µm for 2 marks Allow 1 mark for (104/20)x 5 or (104/20.5) x 5 or (105/20) x 5 or (105/20.5) x 5 104000/ 4000 or 105000/ 4000 or 104000/ 4100 or 105000/ 4100

2 2 2 1

(ii) all from {secondary oocyte/ female/ mother/ egg}(1)

1 1

(iii) 4 correct (2), 2/3 correct (1)

2 2

(iv) {Nucleus/ DNA / nuclear material/ genetic information} from mother/patient (1) {Nucleus/ DNA/ sperm} from father (1) Mitochondria (DNA) from Donor (1)

3 3

(b) (i) Move (from one square to another)(1) 1 1 1

(ii) I II III

10mm 10mm 10mm = 1000/ 1 x 10 3(mm3 )

40 x 1 000 000 = 40 000 000/ 4 x 107 (1) 400 000 x 100 = 4 000 000 000 / 4 x 109 (1) ECF from II

3 3 3 3

Question 3 total 8 4 12 5 5

7 © WJEC CBAC Ltd.



4 (a) (i) Any 3 x (1) from: Random mating (1) non disjunction does not occur/ no mutations (1) Large population (1) No immigration/ no emigration / population is isolated (1) No selection/ selective advantage (1)

3 3

(ii) I

II

III

IV

55% (1)

3 025 (1)

2 025 (1)

4 950 (1)

4 4 4

(b) Genetic drift/ founder effect (1) Emigrated (small) group with an abnormally high frequency of N / abnormally low frequency of M (1) Emigrated population did not mate with general Pennsylvanian population/ no {allele / gene} flow (1)

1 2 3

Question 4 total 3 5 2 10 4

8 © WJEC CBAC Ltd.



5 (a) Soak some seeds in gibberellic acid (1) Measure clear area/ compare size of clear zone (1) Any two from: Same type/ variety/ age/ size/ mass of seed (1) Soaked for same time (1) Same conc./depth starch agar (1) Same temperature/ light (1)

4 4 4

(b) Reject hypothesis/ accept null hypothesis (1) Seeds germinated before increase in amylase (1)

2 2

Question 5 total 6 6 4

9 © WJEC CBAC Ltd.



6 A: Hormonal control of ovulation

FSH stimulates the development of follicles in the ovary.

follicle cells produce oestrogen

which inhibits the production of FSH

and stimulate the production of LH.

LH stimulates production of more oestrogen

and oestrogen stimulates production of LH.

Eventually the LH levels cause ovulation.

increase in FSH levels also aids ovulation.

The corpus luteum produces progesterone.

Which is needed for development of endometrium. B: Similarities

Hormonal control similar for both/ same hormones involved

in both

Copulation affects ovulation

Copulation increases production of LH and FSH

Copulation increases progesterone levels

C: Differences

Rabbits only ovulate after copulation/ In humans ovulation

occurs even if no copulation

Ovulation is not cyclical in rabbits/ ovulation is cyclical in

humans

If no copulation LH and FSH remain low in rabbits

FSH level reach zero in rabbits/ do not reach zero in humans

FSH has single peaks in rabbits/ twin peaks in humans

3

2

4

10 © WJEC CBAC Ltd.



7-9 marks Indicative content of this level is… Detailed explanation of hormonal control . And Similarities And Differences The candidate constructs an articulate, integrated account, correctly linking relevant points, such as those in the indicative content, which shows sequential reasoning. The answer fully addresses the question with no irrelevant inclusions or significant omissions. The candidate uses scientific conventions and vocabulary appropriately and accurately. 4-6 marks Indicative content of this level is… Any two from: Explanation of hormonal control. Similarity Difference The candidate constructs an account correctly linking some relevant points, such as those in the indicative content, showing some reasoning. The answer addresses the question with some omissions. The candidate usually uses scientific conventions and vocabulary appropriately and accurately.




1-3 marks Indicative content of this level is… Brief explanation of hormonal control or A similarity or A difference The candidate makes some relevant points, such as those in the indicative content, showing limited reasoning. The answer addresses the question with significant omissions. The candidate has limited use of scientific conventions and vocabulary. 0 marks The candidate does not make any attempt or give a relevant answer worthy of credit.





7 (a) A disease which is always present at low levels (in an area)/ frequently at a predictable rate in a specific location (1)

1 1

7 (b) (i) A – disulphide bridge/disulphide bond B – Antigen binding site C – Light chain D – Heavy chain All 4 correct = 3 marks, 3 correct = 2 marks, 2 correct =1 mark

3 3

(ii) Antigen –initiates an {immune response/production of antibodies} (1) Antigen-antibody complex- a specific antibody bound to an

antigen/ complementary antibody (1)

2 2

(c) (i) Memory cells (must make IgG during the secondary response/ after second exposure/clonal expansion)(1)

1 1

(ii) Any 2 x (1) from:

The bacteria may have antigenic variation/surface proteins / reference to mutations (1)

(IgM produced again as) no memory cells to new antigen (1)

Primary response each time (1)

2 2

(d) (i) Delay in detection of bacterial antigen /reference to latent period/clonal selection (1) IgG not produced straight away / IgG non existent until day 7/ Time is needed to produce and secrete antibodies (1)

2 2




(ii) Any 5 x (1) from: A. Antibodies maybe already attached to the bacteria/antigen/ a

substance within the plasma (1) B. Different strain of bacteria which is not recognised by the

test (1) C. more than one type of antigen on the surface of the bacteria

(1) D. antibodies not at detectable levels/ Variation amongst

peoples’ immune response/ colour change not detectable (1) E. Enzyme not functioning/denatured (1) F. lack of control of variables e.g. pH/ temperature/ volume of

sample (1)

2 3 5

(e) (i) 35-38 oC and it is a human pathogen/ similar to body temperature (1)

1 1 1

(ii) 380/ 380.13/ 379.94 mm2 = 2 marks

Allow the following for 1 mark 380 (no units) (22/2)2 x 3.14 = (11)2 v 3.14 =

2 2 2

(iii) The zone of inhibition is a perfect circle/ radius is the same all the way round (1)

1 1

Question 7 total 6 9 5 20 2 3




8 (a) (i)

Actin

Myosin Troponin Tropomyosin

A Band

I Band

(1 mark per correct row)

2 2

(ii) Any 2 x (1) from:

Myosin head binds to actin/cross bridges form between actin and myosin (1) Myosin head {bends/tilts/ power stroke} so actin is pulled past the myosin(1) Detail of ATP involvement in release of head (1)

2 2

(b) (i) Calculate a mean to improve reliability / Identify that there were a range of sarcomere lengths (1)

1 1




(ii) 1.2 µm = 3 marks 1.2 (no units) = 2 marks (3.6-1.2) / 2 = 1 mark

3

3 3

(iii) Any 2 x (1) The temperature of solution (1) pH of solution (1) same type of muscle (1) Same concentration solution (1) OR 2 controlled variables without solution (1)

2

2

2

(iv) Any 2 x (1) from:

no overlap between actin and myosin filaments (1)

no cross-bridges form / no possibility of myosin head moving

actin (1)

no contraction possible / sarcomeres cannot get shorter (1)

2

2

(c) (i) each muscle contracts to 'pull' in each direction / as one contracts the other relaxes to move the limb (1)

1 1

(ii) Any 2 x (1) from: Quadriceps contract (1) The osteoarthritic group has a lower contraction force ORA (1)

1 1 2


(iii) Any 5 x (1) from: A. BMI states they are obese / heavier mass to be moved by

quadriceps (1)

B. Reference to BMI and the effect on contraction force/ stair

climb (1)

C. Exercise reduces BMI/ mass(1)

D. Exercise strengthens the quadriceps (1)

E. supports the joint/ strengthens muscles around the joint (1)

F. increases flexibility of the joint / stimulates cartilage growth

/reduces joint stiffness (1)

5 5





9 (a) All three for 1 mark A - Cerebral cortex / cerebrum / frontal lobe B - Cerebellum C - Medulla oblongata

1 1

(b) (i) MRI scan shows {structural anatomy of the brain/pictures which are static} and PET scans shows areas of the brain which are functioning at a particular time (1) MRI wouldn’t show active areas of the brain, as language is an active process (1)

2 2

(ii) Any 5 x (1) from: A. {Broca's area is the same in both / same colour on scan} as

both produce language (1)

B. Increased use of motor cortex in BSL / more activity in that

area in scan (1)

C. because BSL involves more movement than speech alone

(1)

D. Increased {use/ activity} of the occipital lobe for {vision in

BSL / visual stimuli} (1)

E. Decreased use of the auditory cortex in BSL/ less activity in

that area(1)

F. as no link to sound and ear/ no sound detected (1)

2 3 5

(iii) Any 2 x (1) from: Age when became deaf (1) Reason for deafness/ or description of (1) Level of deafness (1)

2 2 2




(iv) Deaf people may exhibit neuroplasticity /'brain has adapted to form new connections as there is no auditory stimuli being received (1) Auditory cortex involved in interpretation of BSL (as near to Wernicke’s area) (1) New connections/different connections to hearing between auditory cortex and {Broca's / Wernicke’s} area (1)

1

2

3

(c) (i) Building a nest / to attract a mate/increase reproductive success / protect offspring/eggs / reduce competition with other males for mating (1)

1 1

(ii) sign stimulus - a stimulus which elicits/causes a FAP (fixed action pattern) in the sticklebacks/ produced by one individual, causes a response in a second individual (1) Red belly triggers the aggressive behaviour/ attack/ bite (1) Data reference twice as many bites seen when red bellied model used/ more aggression seen when red bellied model used (1)

1 2 3

(iii) 5.6 = 2 marks 5.59 = 1 mark

mark 111

3.343

2 2 2

(iv) Reduce confidence in conclusion as SDs overlap (1) 1 1 1



UNIT 4 – VARIATION, INHERITANCE AND OPTIONS SUMMARY OF MARKS ALLOCATED TO ASSESSMENT OBJECTIVES

Question AO1 AO2 AO3 TOTAL MARK MATHS PRAC

Section A

1 4 9 0 13

2 8 7 5 20

3 8 4 12 5 5

4 3 5 2 10 4

5 0 0 6 6 4

6 3 2 4 9

Section A - totals 18 31 21 70 9 9

7 6 9 5 20 2 3

8 6 9 5 20 2 3

9 6 9 5 20 2 3

TOTAL 24 40 26 90 11 12

1400U-4 Biology-Human Biology-Unit4/MS Summer 2017/GH

gce a level marking scheme - cherry hill tuition a2 w june 2017 unit 4 ms.pdf · wjec gce biology -...

Documents